Hvac controller that provides multiple types of proportional motor control signals, an hvac system that includes the same and a proportional control signal circuit

ABSTRACT

The disclosure provides a proportional control signal circuit (PCSC), an HVAC controller employing the same and an HVAC system including the HVAC controller. In one embodiment, the PCSC includes: (1) a signal input configured to receive a pulse width modulated signal, (2) a control input configured to receive an integration signal, (3) a signal output and (4) control circuitry, coupled to the signal input, the control input and the signal output, configured to provide either the pulse width modulated signal or a DC signal to the signal output based on the integration signal.

TECHNICAL FIELD

This application is directed, in general, to controllers or controlboards, such as for heating, ventilating and air conditioning (HVAC)systems, and, more specifically, to reducing the number of dedicatedconnectors on a control board.

BACKGROUND

HVAC systems are used to regulate environmental conditions within anenclosed space. Typically, HVAC systems have a circulation fan thatpulls air from the enclosed space through ducts and pushes the air backinto the enclosed space through additional ducts after conditioning theair (e.g., heating, cooling, humidifying or dehumidifying the air). Todirect operations of the circulation fan and other components, each HVACsystem includes at least one HVAC controller. Traditionally, thecirculation fans in HVAC system were single speed fans that operate inresponse to an on/off signal from the controller. Some HVAC systems,however, include a variable-speed circulation fan that is controlled bya pulse width modulated signal (PWM) from the HVAC controller.

SUMMARY

The disclosure provides a proportional control signal circuit (PCSC) foroperating a motor. In one embodiment, the PCSC includes: (1) a signalinput configured to receive a pulse width modulated signal, (2) acontrol input configured to receive an integration signal, (3) a signaloutput and (4) control circuitry, coupled to the signal input, thecontrol input and the signal output, configured to provide either thepulse width modulated signal or a DC signal to the signal output basedon the integration signal.

In another aspect, the disclosure provides a controller for a heating,ventilating and air conditioning (HVAC) system of an enclosed space. Inone embodiment, the HVAC controller includes: (1) a data reservoirconfigured to store descriptive data about the HVAC system, (2) a signalgenerator configured to provide a pulse width modulated signal tocontrol a device of the HVAC system, and (3) a signal manager configuredto generate an integration signal, based on the descriptive data, tocontrol the pulse width modulated signal.

In yet another aspect, the disclosure provides an HVAC system of anenclosed space. In one embodiment, the HVAC system includes: (1) a motorcontroller for a motor and (2) an HVAC controller configured to providea proportional motor control signal for the motor controller. The HVACcontroller including: (2A) a processor configured to provide a pulsewidth modulated signal to control the motor and an integration signal,based on descriptive data of the HVAC system, to control the pulse widthmodulated signal and (2B) a proportional control signal circuit (PCSC)having a signal input configured to receive the pulse width modulatedsignal, a control input configured to receive the integration signal, asignal output, and control circuitry, coupled to the signal input, thecontrol input and the signal output, configured to provide, based on theintegration signal, to the signal output either the pulse widthmodulated signal or a DC signal as the proportional motor controlsignal.

BRIEF DESCRIPTION

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 illustrates a diagram of an embodiment of a HVAC systemconstructed according to the principles of the disclosure;

FIG. 2 illustrates a block diagram of an embodiment of a controllerconstructed according to the principles of the disclosure;

FIG. 3 illustrates another block diagram of an embodiment of acontroller constructed according to the principles of the disclosure;and

FIG. 4 illustrates a schematic diagram of an embodiment of aproportional control signal circuit constructed according to theprinciples of the disclosure.

DETAILED DESCRIPTION

While some variable-speed motors are controlled by a PWM signal, othervariable-speed motors that are used in HVAC systems operate based on aDC signal. As such, there could be different types of control signalsneeded from an HVAC controller depending on the variable-speed motorthat is used to, for example, control a circulation fan. It is realizedherein the advantage of employing a single controller or control boardfor HVAC systems that can be used for either type of variable-speedmotor. Thus, a company can manufacture a single control board that canbe used with multiple types of HVAC systems. It is further realized,however, that using such a universal controller can require twodifferent types of proportional control signals, dedicated circuitry forthe two types of control signals and dedicated connectors on the controlboard. As such, the flexibility of such a controller also comes withadditional costs.

Accordingly, disclosed herein is a proportional control signal circuit(PCSC) that receives one type of proportional control signal andprovides two different types of proportional motor control signalstherefrom. For example, the received control signal can be a PWM signaland the two control signals can be the PWM signal and a DC voltagesignal. The disclosed integrated circuits advantageously provide auniversal controller without requiring dedicated connectors for thedifferent type of proportional motor control signals. The disclosurefurther provides an HVAC controller that can provide either a PWM or aDC proportional control signal at a single output connector to be usedwith the different types of variable-speed motors of an HVAC component.The HVAC component, for example, can be a circulation fan.

Turning now to FIG. 1, illustrated is a block diagram of an embodimentof a HVAC system 100 constructed according to the principles of thedisclosure. The HVAC system 100 includes a return duct 101, a returnplenum 104, a supply duct 106 and a supply plenum 108. Additionally, theHVAC system 100 includes conditioning systems for cooling and heatingair in the enclosed space. The conditioning systems include a coolingsystem or cooling source 110 and a heating system or heating source 115.The cooling system 110 can include a refrigeration circuit having acompressor system, evaporator coils and condenser coils fluidly coupledtogether. The cooling system 110 has multiple cooling stages. Given theteachings herein, one skilled in the art will understand that thisdisclosure applies to HVAC embodiments having one or more than onecooling stage. The heating system 115 can include a gas furnace,electric heating elements, or even a combination thereof. The heatingsystem 115 can also be multi-staged or a single staged system.

The HVAC system 100 also includes a circulation fan 120, a temperaturesensor 130, a user interface 140 and an HVAC controller 150. Given theteachings herein, one skilled in the art will also understand that theHVAC system 100 may include additional components and devices that arenot presently illustrated or discussed but are typically included in anHVAC system, such as, a humidity sensor, a filter, a power supply, etc.Some of illustrated components of the HVAC system 100 may be containedwithin a single enclosure (e.g., a cabinet). In one embodiment, the HVACsystem 100 is a rooftop unit. The HVAC system 100 can be another type ofcommercial HVAC system or a residential system.

The cooling system 110, the heating system 115 and the circulation fan120, sometimes referred to as an indoor air blower, may be conventionaldevices that are typically employed in HVAC systems. The circulation fan120 may be a variable-speed fan. Depending on the installation, thecirculation fan 120, or the motor of the circulation fan is controlledby a PWM control signal or a DC control signal. Typically, thecirculation fan 120 includes a motor controller (not shown) thatreceives a proportional motor control signal from the HVAC controller150 to direct operation of the circulation fan 120. The proportionalmotor control signal is either a PWM signal or a DC signal. Thus, theHVAC controller 150 can be used in an HVAC system having either type ofvariable-speed motor. Advantageously, this can be done without alteringcircuitry for specific installations or having particular outputconnectors for the two different types of control signals.

The temperature sensor 130 is configured to sense the temperature withinthe enclosed space and send the sensed temperature to the HVACcontroller 150. The HVAC controller 150 receives the sensed temperatureand directs operation of the HVAC system employing the sensedtemperature input. The temperature sensor 130 can be a thermostat thatsenses temperature, receives user inputs, and generates thermostatcalls. In one embodiment, the temperature sensor 130 and the userinterface 140 are an integrated device. In some embodiments, thetemperature sensor 130, the user interface 140 and the HVAC controller150 are a single HVAC device.

The user interface 140 is configured to be an interface between a userand the HVAC system 100. The user interface 140 can be an HVAC devicethat has a primary function of communicating between the HVAC system 100and the user. In some embodiments, the user interface 140 can be anon-HVAC device, such as a smart phone, that includes an applicationwhich allows communication between with the HVAC system 100. There maybe multiple user interfaces 140 for the HVAC system 100. In someembodiments, the temperature sensor 130 and the user interface 140 arealso conventional HVAC devices.

As such, in one embodiment, the user interface 140 includes thetemperature sensor 130, a message screen and an alarm annunciator (suchas a bell, a public-address speaker, a telephone message generator, or acomputer network gateway), is coupled to the HVAC controller 150 andconfigured to allow a user to select a set point indoor temperature andperhaps a system operational mode (i.e., air conditioning, heating orventilation) and also display information about the HVAC system 100,including providing alarms and other messages.

The HVAC controller 150 may include a processor, such as amicroprocessor, configured to direct the operation of the HVAC system100. Additionally, the HVAC controller 150 may include an interface anda memory coupled thereto. The interface may include multiple ports orconnectors for transmitting and receiving external data and data from atleast other components or devices of the HVAC system 100, such as thecooling system 110, the heating system 115 and the circulation fan 120.The memory section may be a conventional memory that is constructed tostore data, such as descriptive data of the HVAC system, and computerprograms.

As illustrated in FIG. 1, the HVAC controller 150 is coupled to thevarious components of the HVAC system 100. In some embodiments, theconnections to all of the components there between are through awired-connection. A conventional cable and contacts may be used tocouple the HVAC controller 150 to the various components of the HVACsystem 100 via a controller interface. In some embodiments, a wirelessconnection may also be employed to provide some of the connections.

The HVAC controller 150 is configured to provide a proportional motorcontrol signal to the circulation fan 120. The proportional motorcontrol signal can be a PWM control signal or a DC control signal. TheHVAC controller 150 includes a single output connector (not shown) thatis dedicated to connect to the circulation fan 120 and provide theproportional motor control signal regardless if a PWM or DC controlsignal is required.

The HVAC controller 150 includes a signal generator 152, a datareservoir 154, a signal manager 156 and a PCSC 158. The signal generator152 is configured to provide a PWM signal to control the circulation fan120. The signal generator 152 can be part of a conventional processor ofan HVAC controller that is used to generate PWM signals as directed inresponse to HVAC programs, user inputs and environmental data of theenclosed space, such as a sensed temperature.

The data reservoir 154 is configured to store descriptive data about theHVAC system 100. The data reservoir 154 may be stored in a conventionalmemory of the HVAC controller 150. In one embodiment, the data reservoir152 is stored as a table in a memory of the HVAC controller 150. In someembodiments, the data reservoir 154 is scalable. The descriptive dataidentifies the type of HVAC system 100 and the various components of theHVAC system 100. For example, the descriptive data includes modelnumbers, configuration numbers and identification numbers of thecomponents of the HVAC system 100.

The signal manager 156 is configured to generate an integration signal,based on the descriptive data, to control the PWM signal generated bythe signal generator 152. The signal manager 156 is configured toanalyze the descriptive data to determine if the proportional motorcontrol signal for the circulation fan 120 should be a PWM signal or aDC voltage signal. In one embodiment, the descriptive data includes amodel number of the circulation fan 120 or a motor of the circulationfan 120 that dictates the required proportional motor control signal.The model number can be assigned during manufacturing. The model numbercan also be used to indicate a frequency or frequencies of the PWMsignal that is generated by the signal generator 152.

The PCSC 158 is configured to receive both the PWM signal from thesignal generator 152 and the integration signal from the signal manager156. Based on the integration signal, the PCSC 158 is configured toprovide the PWM signal as the proportional motor control signal for thecirculation fan 120 or provide a proportional motor control signal thatis a DC voltage signal. In one embodiment, a voltage of the DC motorcontrol signal is determined by a duty cycle of the PWM signal.

FIG. 4 provides additional information of the configuration of anembodiment of a PCSC as disclosed herein and FIGS. 2 and 3 provideadditional information of an HVAC controller as disclosed herein.

Turning now to FIG. 2, illustrated is a block diagram of an embodimentof HVAC controller 200 constructed according to the principles of thedisclosure. The HVAC controller 200 includes an interface 210, aprocessor 230, a memory 220 and a PCSC 240. The interface 210, theprocessor 230, the memory 220 and the PCSC 240 can be connected togethervia conventional means. In one embodiment, the interface 210, theprocessor 230, the memory 220 and the PCSC 240 are each located on onecontrol board of the HVAC controller 200. The control board can be ageneral purpose control board for an HVAC system, such as the HVACsystem 100.

The interface 210 is configured to receive and transmit data for theHVAC controller 200. The interface 210 provides a physical connectionbetween the HVAC controller 200 and components of the HVAC systemconnected thereto. The interface 210 is configured to receive signalsindicating conditions or events or other data associated with the HVACsystem. The signals may be associated with a sensed temperature of theenclosed space, temperature inputs, program inputs, thermostat calls,etc. The interface 210 can be a conventional interface that is used toreceive and transmit data for a controller, such as a micro-controller.The interface 210 can include multiple ports, terminals or connectorsfor receiving or transmitting the data. The ports, terminals orconnectors may be conventional receptacles for communicating data via acommunications network or HVAC data bus.

The memory 220 may be a conventional memory typically located within anHVAC controller that is constructed to store data and computer programs.The memory 220 includes a data reservoir configured to store descriptivedata about the HVAC system. The memory 220 may store operatinginstructions to direct the operation of the processor 230 when initiatedthereby. The operating instructions may correspond to algorithms thatprovide the functionality of the operating schemes disclosed herein. Forexample, the operating instructions may correspond to the algorithm oralgorithms that determine an integration signal based on the descriptivedata. In one embodiment, the memory 220 or at least a portion thereof isa non-volatile memory.

The processor 230 is configured to operate the HVAC system in one of aplurality of conditioning modes, such as a heating mode and a coolingmode, based on, for example, environment data of an enclosed space anddata of the HVAC system. The processor 230 may a microprocessor. Theprocessor 230 is configured to generate a PWM signal that is employed tocontrol a device of the HVAC system, such as a circulation fan. In oneembodiment, the memory 220 or a portion thereof is part of the processor230.

The PCSC 240 is configured to receive a PWM signal and an integrationsignal from the processor 230 and provide a proportional motor controlsignal based thereon. The proportional motor control signal, either aPWM motor control signal or a DC voltage motor control signal, isprovided to the interface 210 for transmission to a motor controller ofthe HVAC system. The motor controller can be for a circulation fan motorof an HVAC system.

Turning now to FIG. 3, illustrated is a block diagram of an embodimentof HVAC controller 300 constructed according to the principles of thedisclosure. The HVAC controller 300 includes an input interface 310, aprocessor 320, a memory 330, a PCSC 340 and an output interface 350. Theinput interface 310, the processor 320, the memory 330, the PCSC 340 andthe output interface 350 can be connected together via conventionalmeans. In one embodiment, the input interface 310, the processor 320,the memory 330, the PCSC 340 and the output interface 350 are eachlocated on one control board 301 of the HVAC controller 300, asindicated by the dashed line. The control board can be a general purposecontrol board for an HVAC system, such as the HVAC system 100. Oneskilled in the art will understand that the HVAC controller 300 caninclude additional components, such as additional operating boards,typically included with a controller of an HVAC system.

The input interface 310 is configured to receive data for the HVACcontroller 300. The input interface 310 is configured to receive signalsindicating conditions or events or other data associated with the HVACsystem. The signals may be associated with a sensed temperature of theenclosed space, temperature inputs, program inputs, thermostat calls,etc. The input interface 310 can be a conventional interface that isused to receive and transmit data for a controller, such as amicro-controller. The input interface 310 can include multiple ports,terminals or connectors for receiving data. The ports, terminals orconnectors may be conventional receptacles for communicating data via acommunications network or HVAC data bus.

The memory 320 may be a conventional memory typically located within anHVAC controller that is constructed to store data and computer programs.In one embodiment, the memory 320 includes a data reservoir configuredto store descriptive data about the HVAC system. The memory 320 maystore operating instructions to direct the operation of the processor330 when initiated thereby. The operating instructions may correspond toalgorithms that provide the functionality of the operating schemesdisclosed herein. For example, the operating instructions may correspondto the algorithm or algorithms that determine an integration signalbased on the descriptive data. In one embodiment, the memory 320 or atleast of portion thereof is a non-volatile memory.

The processor 330 is configured to operate the HVAC system in one of aplurality of conditioning modes, such as a heating mode and a coolingmode, based on the input signals. The processor 330 may amicroprocessor. The processor 330 is also configured to generate a PWMsignal that is employed to control a device of the HVAC system, such asa circulation fan, and an integration signal that is employed to controlthe PWM signal. The processor 330 generates the integration signal basedon the descriptive data. In one embodiment, the processor 330 generatesthe integration signal once. In some embodiments, this occurs duringinstallation. In one embodiment, the memory 320 or a portion thereof ispart of the processor 330.

The PCSC 340 is configured to receive a PWM signal and an integrationsignal from the processor 330 and provide a proportional motor controlsignal based thereon. The PCSC 340 is configured to provide either thePWM signal or a DC voltage signal as the proportional motor controlsignal based on the integration signal.

The output interface 350 is configured to provide a physical connectionbetween the HVAC controller 300 and components of the HVAC systemconnected thereto. The output interface 350 can be a conventionalinterface that is used for the transmission of data from the HVACcontroller 300. The output interface 350 can include multiple ports,terminals or connectors for the transmission of data. The ports,terminals or connectors may be conventional receptacles forcommunicating data via a communications network or HVAC data bus.

In FIG. 3, one connector of the output interface 350, connector 354, isdesignated to provide the proportional motor control signal, whether PWMor DC, to a motor controller 399. The motor controller 399 can be acontroller for a fan motor of the HVAC system, including a circulationfan of the HVAC system, or another type of variable speed motor. Thus,unlike conventional HVAC controllers, the HVAC controller 300 only needsa single connector designated for a particular proportional motorcontrol signal regardless if a PWM or DC control signal is needed. Insome embodiments the HVAC system includes multiple motors that could beeither type of variable-speed motor. As such, in some embodiments, theremay be a PCSC and a designated connector for each such motor controlledby the HVAC controller 300.

FIG. 4 illustrates a schematic diagram of an embodiment of a PCSC 400according to the principles of the disclosure. The PCSC 400 includes asignal input 410, a control input 420, a signal output 430 and controlcircuitry 440. The PCSC 400 also includes an input buffer 450 and anoutput buffer 460.

The signal input 410 is configured to receive a PWM signal via the inputbuffer 450. The input buffer 450 can be a conventional buffer. Thecontrol input 420 is configured to receive an integration signal and thesignal output 430 is configured to provide a connection between the PCSC400 and a connector, such as connector 354 of the output interface 350.The PWM signal and the integration signal can be received from aprocessor of an HVAC controller, such as a microprocessor. The signalinput 410, the control input 420 and the signal output 430 can beconventional terminals employed with integrated circuits.

The control circuitry 440 is connected to the signal input 410, thecontrol input 420 and the signal output 430, and is configured toprovide either the PWM signal or a DC signal to the signal output 430based on the integration signal. The control circuitry 440 includes aresistor 442 connected between the signal input 410 and the signaloutput 420. The control circuitry 440 also includes an integration node444 connected between the resistor 442 and the signal output 430. Thecontrol circuitry 440 further includes a switch 446 connected to groundand a capacitor 448 connected between the switch 446 and the integrationnode 444. The switch 446 can be a FET. The switch 446 is connected tothe control input 420 and is operated based on the integration signal.If the voltage of the integration signal is sufficient to turn-on theswitch 446 (i.e., integration signal is “on”) then the switch 446provides continuity to ground. If the voltage of the integration signalis such that the switch 446 is off (i.e., integration signal is “off”)then the switch 446 provides substantial resistance, e.g., approximatelyinfinite resistance. The capacitor 448 and the resistor 442 provide anintegration function to the received PWM signal when the integrationsignal is “on.” As such, when the integration signal is “on,” theresistor 442 and the capacitor 448 operate as a low pass filter.

In one embodiment, the control circuitry 440 provides the DC signal whenthe integration signal is “on” and the PWM signal when the integrationsignal is “off.” The desired proportional motor control signal ispresented to the motor controller via the connector. If the proportionalmotor control signal is a DC signal, a PWM frequency is chosen. In oneembodiment, the PWM frequency is determined by the requirements of theconnecting device that receives the proportional motor control signal.The desired frequency can be saved as descriptive data in a datareservoir or memory as disclosed herein, and used as needed to configurea signal generator. In one embodiment, the signal generator is a PWMgenerator of a processor such as the processor 230 or 330 disclosedherein. The value of capacitor 448 is chosen to filter ripple offrequencies supported by the signal generator to provide tolerableripple on the charge voltage on the capacitor 448. The average voltageis determined by the duty cycle of the PWM signal. The output buffer 460forwards the DC signal to the motor controller via the connector. Theoutput buffer 460 can be a unity gain impedance buffer. The type andsize of the various components of the control circuitry 440 can varybased on the PWM signal received. The values of the resistor 442 and thecapacitor 448 are selected to provide a low pass filter adequate tofilter frequencies supported by the signal generator.

In the illustrated embodiment, a voltage level of the DC signal isdetermined by a duty cycle of the PWM signal received at the signalinput 410. Three different duty cycles are illustrated in FIG. 4 for thePWM signal: twenty five percent, fifty percent and seventy five percent.Considering, for example, a voltage range of zero to ten volts for theproportional motor control signal, then the twenty five percent dutycycle would provide a 2.5 VDC proportional motor control signal.Additionally, the fifty percent duty cycle would provide a 5.0 VDCproportional motor control signal and the seventy five percent dutycycle would provide a proportional motor control signal of 7.5 VDC.

Those skilled in the art to which this application relates willappreciate that other and further additions, deletions, substitutionsand modifications may be made to the described embodiments.

What is claimed is:
 1. A proportional control signal circuit (PCSC) foroperating a motor, comprising: a signal input configured to receive apulse width modulated signal; a control input configured to receive anintegration signal; a signal output; and control circuitry, coupled tosaid signal input, said control input and said signal output, configuredto provide either said pulse width modulated signal or a DC signal tosaid signal output based on said integration signal.
 2. The PCSC asrecited in claim 1 wherein said control circuitry provides said DCsignal when said integration signal is on and said pulse width modulatedsignal when said integration signal is off.
 3. The PCSC as recited inclaim 1 wherein a voltage level of said DC signal is determined by aduty cycle of said pulse width modulated signal.
 4. The PCSC as recitedin claim 1 wherein said control circuitry includes a resistor connectedbetween said signal input and said signal output.
 5. The PCSC as recitedin claim 4 wherein said control circuitry includes an integration nodeconnected between said resistor and said signal output.
 6. The PCSC asrecited in claim 5 wherein said control circuitry includes a switchconnected to ground and a capacitor connected between said switch andsaid integration node.
 7. The PCSC as recited in claim 1 wherein saidswitch is connected to said control input and is operated based on saidintegration signal.
 8. A controller for a heating, ventilating and airconditioning (HVAC) system of an enclosed space, comprising: a datareservoir configured to store descriptive data about said HVAC system; asignal generator configured to provide a pulse width modulated signal tocontrol a device of said HVAC system; and a signal manager configured togenerate an integration signal, based on said descriptive data, tocontrol said pulse width modulated signal.
 9. The controller as recitedin claim 8 further comprising a proportional control signal circuit(PCSC) configured to provide a proportional motor control signal forsaid device based on said integration signal and said pulse widthmodulated signal.
 10. The controller as recited in claim 9 furthercomprising an output connector connected to said PCSC and configured toprovide said proportional motor control signal to said device.
 11. Thecontroller as recited in claim 8 further comprising a processor, whereinsaid signal generator is a pulse width modulated generator of saidprocessor.
 12. The controller as recited in claim 8 wherein a frequencyof said pulse width modulated signal is based on said descriptive data.13. The controller as recited in claim 8 further comprising an inputinterface coupled to said processor and configured to receiveenvironmental data of said enclosed space.
 14. The controller as recitedin claim 13 wherein said processor is configured to generate said pulsewidth modulated signal based on said environmental data.
 15. A heating,ventilating and air conditioning (HVAC) system of an enclosed space,comprising: a motor controller for a motor; and an HVAC controllerconfigured to provide a proportional motor control signal for said motorcontroller, including: a processor configured to provide a pulse widthmodulated signal to control said motor and an integration signal, basedon descriptive data of said HVAC system, to control said pulse widthmodulated signal; and a proportional control signal circuit (PCSC),including: a signal input configured to receive said pulse widthmodulated signal; a control input configured to receive said integrationsignal; a signal output; and control circuitry, coupled to said signalinput, said control input and said signal output, configured to provide,based on said integration signal, to said signal output either saidpulse width modulated signal or a DC signal as said proportional motorcontrol signal.
 16. The HVAC system as recited in claim 15 wherein saidproportional motor control signal is said DC signal when saidintegration signal is on.
 17. The HVAC system as recited in claim 15wherein a voltage level of said DC signal is determined by a duty cycleof said pulse width modulated signal.
 18. The HVAC system as recited inclaim 15 wherein a frequency of said pulse width modulated signal isdetermined by said descriptive data and environmental data of saidenclosed space.
 19. The HVAC system as recited in claim 15 wherein saidsignal output is a single connection terminal for said pulse widthmodulated signal or said DC signal as said proportional motor controlsignal.
 20. The HVAC system as recited in claim 15 wherein said controlcircuitry includes a resistor connected between said signal input andsaid signal output, an integration node connected between said resistorand said signal output, a switch connected to ground, and a capacitorconnected between said switch and said integration node, wherein saidswitch is connected to said control input and is operated based on saidintegration signal.